The major group of rhinoviruses are responsible for 36 to 45% of all common colds, tens of millions of lost school and work days, billions of dollars of doctor's office visits and over-the-counter remedies, secondary bacterial infections, and exacerbations of respiratory diseases. We will use the cellular receptor for the major group of rhinoviruses, ICAM-1, to develop novel drugs for viral therapy and prophylaxis. ICAM-1 is a single chain molecule with 5 immunoglobulin-like domains and a membrane anchor. We have previously shown that recombinant, 5 domain, soluble ICAM-1 inhibits virus binding and cytopathic effect in vitro, and that the two N-terminal Ig-like domains are required for proper conformation of the virus-binding site in the first domain. Testing different eukaryotic and prokaryotic expression systems, we will determine the optimal truncation position and conditions for obtaining a recombinant two domain ICAM-1 fragment with anti-viral activity, and will test both nonglycosylated and glycosylated derivatives. Material that is optimal for crystallization will be produced in large quantity for determination of its three dimensional structure. This information will be useful for design of small drugs that mimic ICAM-1 and occupy its binding site on the virus. Multivalent, higher avidity ICAM-1 immunoadhesin chimeras will be constructed that splice two or five Ig-like domains of ICAM-1 to Fc regions of IgM, IgA1, or IgG1. The hypothesis will be tested that multivalenty confers high affinity binding to virus and ability to neutralize and induce eclipse at low concentration. The electron microscope will be used to visualize the location of the hinge region of ICAM-1, the shape of immunoadhesins, and interaction with virus. The mechanism of virus entry of host cells will be studied, and the hypothesis tested that multivalent receptor binding and acidic pH represent the events during endocytosis that trigger virus penetration and uncoating. Eclipse is an irreversible mechanism for virus neutralization, and the hypothesis will be tested that this is the mechanism of inactivation by, ICAM-1, and that multivalent ICAM-1 is superior. Soluble receptor-resistant mutants of rhinovirus will be isolated, and the hypothesis tested that these occur at much lower frequency, if at all, with multivalent recombinant ICAM-1 that more closely mimics the avidity of receptor displayed on the cell surface. Plans for further study and cooperation with NIAID staff are discussed.